1. Field of the Invention
The present invention relates to a portable terminal such as cellular phones, Personal Digital Assistants (PDA), Personal Communication System (PCS), game phones, camera phones, Digital Multimedia Broadcasting (DMB) phones, and more particularly to a portable terminal having a lighting function to enable a user to dial another user at night.
2. Description of the Related Art
In general, “a portable terminal” implies an electronic device that a user can carry for communication with another user wirelessly. In consideration of portability, the design of such a portable terminal focuses not only toward a compactness, slimness, and lightness, but also toward providing multimedia capabilities to allow the user to enjoy a wider variety of functions. Thus, future portable terminals will be used in a multimedia environment to provide the Internet access and its related functions globally.
Currently, a conventional portable communication terminal allows a voice communication as well as a high-speed data communication. Further, as consumer's demands have increased, various services have been provided using a wireless communication technology for transmitting and receiving data at a high speed. Most portable terminals are now equipped with an embedded or an external camera lens to transmit image signals and the like.
The portable terminal typically includes data input and output units, data transmitting and receiving units, an antenna unit and the like. The data input unit includes a keypad assembly or a touch screen to input data. The keypad assembly is constructed with key buttons, silicon rubber, dome switches and the like. A well-known liquid crystal display unit is generally used as data output unit.
Moreover, the portable terminal has a lighting device for lighting the keypad and may include a plurality of light emitting diodes arranged on a printed substrate, or an inorganic electro luminescent body inserted in an elastic pad disposed on the printed substrate. FIG. 1 shows such a conventional keypad assembly 100, which includes a switch substrate 120, a plurality of light emitting diode 122, and a keypad 110.
The keypad 110 is made from an elastic material, i.e., silicon and other material made from the combination of silicone and a poly urethane film. The keypad 110 includes a plate-shaped elastic layer 111, a plurality of key buttons 112 having characters printed thereon and mounted on the elastic layer 111, and a plurality of protuberances 111a formed at a lower surface of the key pad 110. The key buttons 112 and the protuberances 111a are vertically aligned to each other.
The switch substrate 120 includes a plate-shaped printed substrate 120a and a plurality of switches 121 facing the protuberance 111a of the keypad 110. Each of the switches 121 is provided with a conductive contact and a metal dome entirely covering the conductive contact. The light emitting diodes 122 are disposed at predetermined positions on the printed substrate 120a. 
However, in order to guarantee the operation of the switch 121, the light emitting diodes 122 are disposed on the printed substrate 120a, each of which is not vertically aligned to the corresponding key button 112. That is, the light emitting diodes 122 are disposed between the switches 121. As a result, the light emitted toward the respective key button 112 from the light emitting diode 122 diverges in all directions, so that the illumination of the key buttons 112 becomes non-uniform and dark. That is, as the light emitted from the light emitting diode is shed through the side of each key button, the number or characters printed on the respective key button cannot be displayed with a uniform brightness.
Therefore, in order to overcome the above-mentioned problems, it is necessary to use a larger number of light emitting diodes for lighting the key buttons, which increases the cost for assembling the light emitting diodes as well as electric power consumption of the light emitting diodes, thereby causing the manufacture of the keypad assembly to be economically inefficient.